This new proposal is submitted in response to NIMH RFA MH-01-002 "Research on depression comorbid with externalizing problems in children." We request two years of funding to conduct the first test-retest reliability and validity study of a parent-report preschool psychiatric diagnostic interview suitable for assessment of comorbidity in very young children - the Preschool Age Psychiatric Assessment (PAPA). No reliability or validity data are available for any diagnostic interview for preschoolers. Knowledge about the onset, presentation and development of comorbid psychiatric disorders in very young children cannot proceed without a reliable and valid diagnostic measure. The aims of this study are to examine the reliability of DSM-IV and DC:0-3 diagnoses and symptom scale scores obtained with the PAPA, investigate the concurrent validity of the PAPA in relation to the Child Behavior Checklist (CBCL), and provide preliminary data about parent-reported comorbidity between affective symptoms, syndromes, and disorders, and disruptive symptoms, syndromes, and disorders in preschool children. We will recruit and screen 1,625 parents of children ages 2 through 5 years old who attend the Duke Children's Primary Care pediatric clinic. The screening and test-retest/validity phases of the study will be completed in 17 months. At the pediatric clinic, the parent will complete the CBCL/1 1/2-5, a revised version of the preschool version of the CBCL. A child will be "screen positive" if s/he scores in the clinical or subclinical range on the CBCL's total problem behaviors scale (at or above the 83rd percentile). We anticipate a screening refusal rate of 10 percent and a test-retest/validity refusal rate of 20 percent. We will recruit 208 parents of screen-positive children and 96 parents of screen-negative children for the test-retest and validity components of the study. We will interview the parent with the Preschool Age Psychiatric Assessment (PAPA) twice with a week between assessments. The CBCL will be re-administered at the first PAPA interview. Interviewers will be blind to the screen status of the subjects. Each of the two PAPA interviews for each subject will be conducted by different interviewers.